When designing an automated semiconductor substrate handler, three main concerns prevail; 1) substrate handler reliability; 2) substrate handler particle generation and potential for substrate contamination; and 3) substrate handler size. Each of these concerns is essentially aimed at reducing costs associated with damaged or defective substrates. Increasing substrate handler reliability prevents substrate damage which can occur when a substrate is incorrectly grasped, etc., and prevents downtime associated with repair and/or recalibration. Reducing particle generation helps reduce defects which result when particles contact substrate surfaces, and reducing substrate handler size allows processing chamber openings to be smaller and to thereby reduce the possibility of particle entry to the chamber and the possibility of substrate contamination thereby.
A major source of particles results when a substrate slides along the surface of the substrate handler""s end effector. Accordingly, after a wafer is placed/loaded onto an end effector, a pin or other holding mechanism conventionally moves into place to secure the substrate and prevent the substrate from sliding against the end effector during transport. However sliding and the particles that result therefrom, may occur as part of the loading process. Further, the holding mechanisms, being moving parts themselves, can generate particles and can introduce reliability issues, increasing substrate handler costs. Moreover, during the entire load and transfer process, particles and other contaminants may collect on the substrate or between the end effectors and the substrate.
Accordingly, a need exists for an improved substrate handler, and particularly for a substrate handler having an improved end effector which will reduce substrate sliding and the associated need for moving parts to control substrate sliding. Such a substrate handler and end effector should be streamlined, and should reduce the probability of contaminant contact with substrate surfaces and/or the probability of trapped contaminants between the end effector and the substrate.
The present invention provides an inventive gripper assembly having a pair of fingers operatively coupled to the gripper so as to move between an open and a closed position; each finger has an end effector coupled thereto, and adapted to support a vertically oriented substrate therebetween. Each end effector has a first pair of opposed surfaces and a second pair of opposed surfaces. Each pair of opposed surfaces is adapted either to simultaneously contact the edge of a vertically oriented substrate supported by the end effector, (clamp-type contact) or to limit horizontal movement of a vertically oriented substrate supported by the end effectors (pocket-type contact). Each of the opposed surfaces preferably does not move relative to the other. A pair of opposed surfaces that do not move relative to each other is referred to herein as unitary, whether made of one or more pieces. Preferably, both the first and second opposed surfaces are radiused to mimic the circumference of the wafer so as to deter fluid and contaminants from collecting between the substrate and the surfaces of the end effector.
In operation, the end effectors are positioned on opposite sides of a vertically oriented substrate, and preferably pick up or grasp the substrate in either of the two manners described below. Specifically, in the case of a gripper assembly configured for clamp-type contact, the end effectors are moved to a position at which the end effectors may stabily support the vertically oriented substrate. Thereafter, the end effectors are closed such that the end effector""s first and second pairs of opposed surfaces contact the substrate""s edge and thereby support the substrate.
Similarly, in the case of a gripper assembly configured for pocket-type contact, the gripper assembly may simply close such that the two pairs of opposed surfaces positioned closest to the bottom edge of the substrate contact the substrate. Alternatively, the pocket-type end effectors may move to a position in line with the substrate, yet at an elevation below which the pair of opposed surfaces would contact the substrate when the end effectors are in a closed position. This elevation may be entirely below the substrate or anywhere below the substrate""s horizontal diameter. Thereafter the closed pair of end effectors are elevated such that the end effectors"" lower pairs of opposed surfaces contact and support the substrate via the substrate""s edges. Note that a pocket type gripper need not have an open and closed position, as the gripper may pick up and deposit a substrate by raising and lowering around the substrate as will be apparent with reference to the detailed description of the preferred embodiments.
The clamp-type gripper is advantageous because it is able to grasp wafers that are within a relatively wide tolerance of a desired position, and thus reduces the time required for initial robot calibration and chamber alignment, as well as reducing the frequency and time required for recalibration and alignment.
The pocket-type gripper is advantageous because it reduces the risk of substrate damage. The pocket-type grippers close below the substrate forming a pocket, and then elevate such that the substrate gently contacts the bottom of the pocket (e.g., contacts the lower pair of opposed surfaces), and such that the upper pair of opposed surfaces surround the substrate and prevent the substrate from excessive tilting in the horizontal direction. Accordingly, the only force applied to the substrate is a purely vertical lifting force, which tends to generate fewer particles than do multidirectional forces. Further, because there is no external force opposing the vertical lifting force, the substrate is not acted on by external opposing forces, and is less likely to be damaged.
When the gripper assembly is configured such that the gripper is at a higher elevation than the end effectors, the fingers are preferably bent such that the gripper is positioned to the front, back or most preferably the side of the substrate rather than directly above the substrate. Thus, particles from the gripper are less likely to contaminate the substrate.
The end effectors of the inventive gripper assembly, whether clamp-type or pocket-type, preferably have no moving parts, and are therefore inexpensive and less likely to malfunction. Further, the absence of moving parts enable a streamlined design, which in addition to the fact that the gripper assembly grasps a substrate by the substrate""s edges, allows the inventive gripper assembly to move substrates through narrow openings such as those found in semiconductor manufacturing equipment.
Because the inventive gripper assembly is streamlined and inexpensive, and because the gripper assembly experiences reduced calibration time, reduced particle generation, and reduced risk of substrate damage, a substrate handler employing the inventive gripper assembly is ideally suited for semiconductor applications. Moreover, because the inventive gripper assembly supports a substrate in a vertical orientation, contaminants are less likely to collect on the substrate""s surfaces. Further contamination reduction may be achieved with the use of radiused end effector surfaces which are radiused to mimic the circumference of the wafer, and thus may minimize or eliminate contact with the front or back surface of the wafer and may contact only the beveled edge of the wafer.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.